Method for Making Metal Wire for Wire Electrical Discharge Machining and the Metal Wire Product Thereof

ABSTRACT

A method for making a metal wire adapted for wire electrical discharge machining, comprises the steps of:
     A. Preparing a brass core wire having a diameter of at least 1.2 mm and having a zinc content of less than 40% by weight;   B. Plating at least a coating material of zinc alloy having a zinc content of more than 75% by weight on the brass core wire to form a coating layer on the core wire so as to form a coarse wire by a spray plating process by atomizing and depositing a plurality of zinc alloy particles of the coating material on at least a surface portion of the brass core wire to form a plurality of cleavages or cavities on or in an outer surface of the coating layer of the coarse wire; and   C. Drawing or stretching the coarse wire to obtain a metal wire product having a diameter ranging from 0.15 mm through 0.35 mm.

RELATED APPLICATION

This application claims the benefit of a Taiwanese patent application, Appl. No. 108111963, filed on Apr. 3, 2019, the specification of which is incorporated here by this reference.

BACKGROUND OF THE INVENTION

In performing a wire electrical discharge machining (wire EDM), a brass wire serving as an electrode wire is opposed to and separated from a workpiece with a suitable gap, adapted for causing electric discharge between the wire (electrode) and the workpiece through a dielectric medium, whereby upon electrical discharging, the workpiece will be cut or shaped in accordance with a predetermined pattern.

However, brass particles or debrises after vaporization of the dielectric medium will be deposited or accumulated on a machining surface of the workpiece, thereby disqualifying the properties including surface hardness, roughness, and thickness of the workpiece. Furthermore, when the brass debrises block the gap between the wire electrode and the workpiece, a short circuit may occur to interrupt the machining work, and a cooling as flushed by the fluid will stop, thereby possibly causing breakage of the brass wire.

The present inventor has found the drawbacks of the conventional wire EDM and invented the present method for well making a metal wire for improving the wire EDM.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for making a metal wire adapted for wire electrical discharge machining or wire EDM, comprising the steps of:

-   A. Preparing a brass core wire having a diameter of at least 1.2 mm     and having a zinc content of less than 40% by weight; -   B. Plating at least a coating material of zinc alloy having a zinc     content of more than 75% by weight on the brass core wire to form a     coating layer on the core wire by a spray plating process by     atomizing and depositing a plurality of zinc alloy particles of the     coating material on at least a surface portion of the brass core     wire to form a plurality of cleavages or cavities on or in an outer     surface of the coating layer of the coarse wire; and -   C. Drawing or stretching the coarse wire to obtain a metal wire     product having a diameter ranging from 0.15 mm through 0.35 mm.

The spray plating process may include plating a coating layer comprised of at least two zinc alloys having different zinc contents in the coating layer on the brass core wire. After atomizing or depositing the coating layer on the brass core wire, different zinc alloy particles will be presented on the outer surface portion of the coarse wire. The zinc alloy may also be substituted with pure zinc metal.

When performing the spray plating, the brass core wire is preheated to 350° C.˜420° C. to help an easier adhesion or coating of the atomized particles of the coating layer to thereby foam a stable coating layer and also be beneficial for forming alpha plus beta (α+β) bidirectional crystal structures between the brass core wire and the coating layer.

In the present invention, the metal wire product is drawn or stretched from the original coarse wire (or “mother” wire) by the following steps:

-   A. In 100° C.˜150° C., a coarse wire (or mother wire) is formed to     have a diameter of 0.8 mm via a pre-drawing process (not shown); -   B. In normal temperature to 300° C., the coarse wire is drawn or     stretched to have a diameter of 0.15 mm˜0.35 mm, and -   C. In normal temperature to 300° C., the coarse wire as previously     drawn is annealed for 1˜5 hours.

Since the zinc alloy will be broken during the drawing or stretching process, the coarse wire when drawn to have a diameter of 0.15 mm˜0.35 mm, cleavages or cavities will be formed on the surface of the coarse wire. Such cleavages or cavities have the following advantages:

-   1. The cleavages or cavities as recessed in the wire surface will     increase the contact area with the dielectric medium or fluid to     facilitate the heat dissipation or cooling, thereby increasing the     efficiency of wire EDM. -   2. The debrises produced during the cutting process may be easily     flushed or removed by the dielectric fluid, thereby preventing wire     breakage and enhancing a smooth processing of the wire EDM. -   3. A short circuit between the wire and the workpiece may be     eliminated to minimize the interruption of machining operation.

During the annealing process for making the metal wire of the present invention, the metal wire may approach an induction coil having a voltage of 110V˜240V to orient the crystals of zinc oxide of the coating layer to be in an identical crystal direction for helping formation of crystal layer with pyroelectricity for enhancing the efficiency of wire EDM.

During the spray plating process of the present invention, a plurality of rollers is provided for guiding the wire to be plated smoothly. The plating process may also be repeated for several cycles for completely plating plural coating layers on the core wire.

The thickness of the coating layer as plated on the coarse wire (or mother wire) may range from 10 μm˜100 μm (micrometers).

Another object of the present invention is to provide a metal wire for wire electrical discharge machining (wire EDM) comprising: a brass core wire having zinc content of less than 40% weight; a coating layer disposed around or surrounding the core wire to form a coarse wire having a zinc content of more than 75% by weight in the coating layer which and having cleavages or cavities formed on a surface of the coarse wire; and a crystal layer of pyroelectricity formed on an outer surface of the coarse wire.

The present invention may be hereinafter described in detail with reference to the drawings accompanied herewith.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of the process steps of the present invention.

FIG. 2 shows a wire as guided by plural rollers to be spray plated in accordance with the present invention.

FIG. 3 shows the wire being repeatedly spray plated as guided by plural rollers.

FIG. 4 is a sectional drawing illustrating the profile of the metal wire after being spray plated in accordance with the present invention.

FIG. 5 is an enlarged view of the metal wire through a microscope.

FIG. 6 shows another metal wire as plated by a coating material of zinc alloy containing two different zinc contents.

FIG. 7 is an enlarged view through a microscope of a metal wire containing zinc alloy having two different zinc contents.

DETAILED DESCRIPTION

As shown in FIGS. 1˜4, the present invention discloses a method for making a metal wire adapted for wire electrical discharge machining (wire EDM). According to the present invention, a brass core wire 10, having zinc content less than 40% by weight and having a diameter of at least 1.2 mm, is plated by spray plating process with a coating layer 20 of zinc alloy having zinc content more then 75 % by weight. The spray plating process may also be repeated for well coating of the zinc alloys on the core wire. The zinc alloy of the coating layer 20 will be atomized through the spray plating process to deposit or stack a plurality of zinc alloy particles on the core wire 10 to form a coarse wire (or mother wire) L′. The coarse wire L′ will then be stretched or drawn to be a metal wire L having a diameter of 0.15˜0.35 mm.

As shown in FIGS. 1, 4, and 5, the coating material of zinc alloy, after being atomized, will be presented as a coating layer 20 having a plurality of zinc alloy particles 21 stacked or mingled having apertures defined among the particles on the brass core wire 10. Among the particles 21 of zinc alloy, cleavages or cavities C will be formed as shown in FIG. 5 when the coarse wire L′ is drawn or stretched.

As shown in FIGS. 1, 6, and 7, the coating material of zinc alloy contains at least two different zinc contents (>75%) with each other. After spray plating, the particles 21 a, 21 b of different zinc contents will be atomized and deposited on the core wire 10. Due to different zinc contents of the zinc alloy, different physical or mechanical properties such as ductility will be presented, thereby helping formation of cleavages or cavities C on the coating layer 20. For instance, the high-ductility zinc alloy particles will be quickly drawn to be separated from the low-ductility zinc alloy particles, thereby causing cavities C therebetween. Such cavities C may enhance heat dissipation, help flushing and removing of debrises produced in the machining, prevent breaking of wire, and increase efficiency of wire EDM.

The core wire 10 may be pre-heated to 350° C.˜420° C. to increase the surface temperature of the core wire to approach the melting point of the coating material of zinc alloy, thereby increasing the adhesion or deposition of the coating material on the core wire.

According to the present invention, the coarse wire L′ is drawn at temperature of 100° C.˜150° C. to have a diameter of 0.8 mm at the primary drawing step. Then, the wire is further drawn at the secondary drawing step to have a diameter of 0.15 mm˜0.35 mm under 200° C.˜300° C., and then annealed for 1˜5 hours to obtain the metal wire (L) product.

The aforementioned primary drawing step at 100˜150° C. is provided to obtain a better ductility of the coating layer 20 to get a smooth appearance of the drawn wire. The secondary drawing step is conducted under normal temperature or under 220° C.˜300° C. to draw the wire to have a diameter of 0.15 mm˜0.35 mm. Through such a secondary drawing step, cleavages or cavities C will be formed on the surface of the coating layer for increasing the efficiency of wire EDM, which is novel and not anticipated by the prior arts. Depending upon the practical requirements, the diameter of the metal wire may include: 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, and 0.35 mm , but not limited in this invention.

During the annealing process step of the present invention, the metal wire may be moved to approach an induction coil to re-arrange the crystal orientations of the coating layer 20 to orient the crystal direction of the coating layer of zinc alloy (zinc oxide) to be an identical direction, thereby forming a crystal layer of pyroelectricity on an outer surface of the coating layer so as to increase the efficiency of wire EDM.

The spray plating process as shown in FIG. 2 discloses a core wire 10 which is pulled by a plurality of rollers 30 and is plated with coating layer by a spray nozzle N (having heat applied to melt the coating material for spraying) within a spray plating zone S to form a coarse wire L′, which is further drawn to be a metal wire product L. As shown in FIG. 3, the wire is repeatedly plated by the spray nozzle N within the spray plating zone S. For example, the upper wire section L′u after being plated is rewound to be a lower wire section L′d as positioned under the upper wire section L′u so as to repeatedly plate the wire for increasing the plating thickness or homogeneity. The plating process may be repeated in several times, depending upon the practical production requirements, such as consideration of the plating thickness or homogeneity of the wire.

The plating thickness on the coarse wire may be 10 micrometers (μm) ˜100 micrometers (μm), preferably being 10 μm˜30 μm.

As shown in FIGS. 4˜7, the metal wire of the present invention comprises: a core wire 10, a brass wire having zinc content less than 40% by weight; and a coating layer 20 of zinc alloy having zinc content more than 75% by weight and comprising a plurality of zinc alloy particles adhered or deposited on or around the surface of the core wire 10, after being atomized by the spray plating process, to be a coarse wire after the spray plating process. The coarse wire is further drawn or stretched to be a fine or thin metal wire product of the present invention having cleavages or cavities C recessed in the surface of the coating layer 20.

The coating layer 20 of the metal wire when annealed, is moved to approach an induction coil to further form a crystal layer of pyroelectricity on the outer surface of the metal wire.

As shown in FIGS. 6 and 7, the coating material of zinc alloy for the coating layer 20 may be comprised of at least two zinc alloys having different zinc contents with each other so that there are at least two kinds of zinc alloy particles 21 a, 21 b, when atomized during spray plating process, being deposited on the wire.

The thickness of the coating layer 20, before being stretched, is ranging from 10 μm˜100 μm, but preferably ranging from 10 μm˜30 μm.

The present invention may be further described in detail in the following Examples:

Example 1

A brass core wire 10 having a zinc content of 37% (by weight) and diameter of 1.2 mm is chosen. A coating material of zinc alloy having zinc content of 95% by weight is plated on the brass core wire 10 by spray plating process to form a coating layer 20 of the zinc alloy on the core wire 10, having a thickness (average) of coating layer of 25 μm. At 120° C., the zinc-coated wire is drawn or stretched to be a thinned wire with 0.8 mm diameter. Then, the wire is further stretched, at 250° C., to have a diameter of 0.25 mm. At 250° C., the stretched wire is annealed for 2.5 hours to obtain the metal wire product L of this invention. Such a metal wire is tested to have a tensile strength of 1015 N/mm² and is successfully meeting the requirement for wire EDM.

Example 2

A brass core wire 10 having a zinc content of 37% (by weight) and diameter of 1.2 mm is chosen. A coating material of zinc alloy having zinc content of 95% by weight is plated by twice on the brass core wire 10 by spray plating process to form a coating layer 20 of the zinc alloy on the core wire 10, having a thickness (average) of coating layer of 50 μm. At 120° C., the zinc-coated wire is drawn or stretched to be a thinned wire with 0.8 mm diameter. Then, the wire is further stretched, at 250° C., to have a diameter of 0.25 mm. At 250° C., the stretched wire is annealed for 1.5 hours to obtain the metal wire product L of this invention. Such a metal wire is tested to have a tensile strength of 1010 N/mm² and is successfully meeting the requirement for wire EDM.

Example 3

A brass core wire 10 having a zinc content of 32% (by weight) and diameter of 1.2 mm is chosen. A coating material of zinc alloy having zinc content of 95% by weight is plated on the brass core wire 10 by spray plating process to form a coating layer 20 of the zinc alloy on the core wire 10, having a thickness (average) of coating layer of 10 μm. At 120° C., the zinc-coated wire is drawn or stretched to be a thinned wire with 0.8 mm diameter. Then, the wire is further stretched, at 250° C., to have a diameter of 0.25 mm. At 250° C., the stretched wire is annealed for 2.5 hours to obtain the metal wire product L of this invention. Such a metal wire is tested to have a tensile strength of 950 N/mm² and is successfully meeting the requirement for wire EDM.

Example 4

A brass core wire 10 having a zinc content of 37% (by weight) and diameter of 1.2 mm is chosen. A coating material of zinc alloy having zinc content of 95% by weight is plated on the brass core wire 10 by spray plating process to form a coating layer 20 of the zinc alloy on the core wire 10, having a thickness (average) of coating layer of 30 μm. At 120° C., the zinc-coated wire is drawn or stretched to be a thinned wire with 0.8 mm diameter. Then, the wire is further stretched, at 250° C., to have a diameter of 0.35 mm. At 250° C., the stretched wire is annealed for 1.5 hours to obtain the metal wire product L of this invention. Such a metal wire is tested to have a tensile strength of 1050 N/mm² and is successfully meeting the requirement for wire EDM.

The present invention discloses a novel spray plating process, without disposal of poisonous waste liquid as found in a conventional electroplating process, thereby causing no pollution problem, and being beneficial for environment protection. Also, the production cost will be greatly reduced, being rich of commercial value.

The present invention may be further modified without departing from the spirit and scope of the present invention. 

I claim:
 1. A method for making a metal wire adapted for wire electrical discharge machining, comprising the steps of: A. Preparing a brass core wire having a diameter of at least 1.2 mm and having a zinc content of less than 40% by weight; B. Plating at least a coating material of zinc alloy having a zinc content of more than 75% by weight on the brass core wire to form a coating layer on the core wire so as to form a coarse wire by a spray plating process by atomizing and depositing a plurality of zinc alloy particles of the coating material on at least a surface portion of the brass core wire to form a plurality of cleavages or cavities on or in an outer surface of the coating layer about the core wire; and C. Drawing or stretching the coarse wire to obtain a metal wire product having a diameter ranging from 0.15 mm through 0.35 mm.
 2. A method according to claim 1, wherein said spray plating process comprises plating a coating layer comprised of at least two zinc alloys having different zinc contents in the coating layer on the brass core wire, whereby upon atomizing or depositing the coating layer on the brass core wire, different zinc alloy particles will be presented on the outer surface of the coating layer of the coarse wire.
 3. A method according to claim 1, wherein said the brass core wire is preheated to 350° C.˜420° C. before being spray plated.
 4. A method according to claim 1, wherein said coarse wire is stretched to have a diameter of 0.8 mm in a temperature range of 100˜150° C., then stretched, at normal temperature or in a temperature range of 200˜300° C., to have a diameter of 0.15˜0.35 mm, and further annealed in a temperature range of 250° C.˜350° C. for 1˜5 hours to obtain the metal wire product.
 5. A method according to claim 4, wherein said metal wire, when being annealed, is moved to approach a magnetic field of an induction coil.
 6. A method according to claim 1, wherein said brass core wire is guided by a plurality of rollers to be spray plated within a spray plating zone for one time or plural times of the spray plating process.
 7. A method according to claim 1, wherein said coating layer on said core wire has a thickness of 10 μm˜100 μm.
 8. A metal wire adapted for wire electrical discharge machining comprising: a brass core wire having a zinc content less than 40% by weight; and a coating layer coated, by a spray plating process, on said core wire to form a coarse wire, said coating layer having a zinc content more than 75% by weight and including a plurality of zinc alloy particles stacked and deposited on said core wire; said coating layer having cleavages or cavities formed on an outer surface of the coating layer upon stretching or drawing of said coarse wire.
 9. A metal wire according to claim 8, wherein said coating layer further comprises an outer crystal layer of pyroelectricity upon approating an induction coil.
 10. A metal wire according to claim 8, wherein said coating layer comprises a zinc alloy containing at least two different zinc contents therein, whereby upon atomizing during the spray plating process, a plurality of zinc alloy particles of at least two different zinc contents will be stacked and deposited on the core wire. 